Work out dynamodb capacity units instantly with clear inputs, formula shown and shareable results.
A read capacity unit covers one strongly consistent read of up to 4 KB, halved for eventually consistent reads and doubled for transactional ones. A write capacity unit covers one write of up to 1 KB, so writes are far more expensive per byte — a 6 KB item costs 6 WCU to write but only 1.5 RCU to read eventually consistently.
Capacity units
RCU = reads x ceil(item KB / 4) x consistency multiplier (0.5 eventual, 1 strong, 2 transactional); WCU = writes x ceil(item KB) x (2 if transactional)
The write unit granularity is 1 KB against 4 KB for reads, and writes must be replicated durably across three availability zones before acknowledgement.
Yes. Capacity consumption is proportional to item size, so splitting rarely accessed attributes into a separate item or into object storage reduces cost substantially.